Adjusting device for a camshaft of an internal combustion engine

ABSTRACT

In an adjusting device for a camshaft of an internal combustion engine having a drive element which is driven by a crankshaft of the internal combustion engine, an output element which drives the camshaft of the internal combustion engine, and an actuating element controlled by a brake so as to provide for a relative rotation between the drive element and output element by varying the braking torque effective on the actuating element.

This is a Continuation-In-Part Application of International Application PCT/EP2004/012536 filed Nov. 5, 2004 and claiming the priority of German Application 103 55 560.9 filed Nov. 28, 2003.

BACKGROUND OF THE INVENTION

The invention relates to an adjusting device for a camshaft of an internal combustion engine with a drive element driven by the crankshaft of the engine and capable of changing the angular position of the camshaft relative to the crankshaft.

DE 100 38 354 A1 discloses an adjusting device for a camshaft of an internal combustion engine which is composed of a planetary summing gear mechanism and an electric servo-motor. One of the two inputs of the gear mechanism is connected to the crankshaft of the internal combustion engine, and the other input is connected to the servomotor. The camshaft is mounted on the output of the gear mechanism. When the rotational speed of the servomotor changes, the rotational speed of the camshaft is changed compared to the crankshaft and the phase angle of the camshaft with respect to the crankshaft is adjusted. However, in order to implement this solution, a two-stage gear mechanism with a high transmission ratio is required, which entails increased costs. In addition, relatively high currents flow during the adjustment, making a power output stage necessary.

DE 102 47 650 A1 discloses an adjustment device of the generic type for a camshaft of an internal combustion engine. The adjusting device has a drive element which is connected fixedly for rotation with the crankshaft, and an output element which is arranged on the camshaft side. In order to adjust the phase angle between the drive element and output element, an actuating element, which is embodied as a lever mechanism, is arranged between the two elements, with a brake acting on the actuating element. However, the lever mechanism is relatively complex and very sensitive to wear and also only permits a limited adjustment range. As a result of the direct connection of the camshaft to the crankshaft, the rotor of the brake, which is connected to the actuating element or the lever mechanism, must run with a constant phase angle and at the same rotational speed (transmission ratio 1:1) as the camshaft. Owing to the transmission ratio of the input and output elements, components are necessary for the adjustment in both directions. The adjustment of the phase angle is performed by braking or accelerating the rotor. In order to be able to rotate the camshaft for advancing the crankshaft, i.e. accelerate the rotor, a rotational spring is additionally located on the actuating element and its continuously acting torque has to be additionally counteracted by braking when the phase angle is constant or when retarding is desired and this additional braking adversely affects the efficiency of the engine.

For the general technical background, reference is made to DE 102 47 54 A1, DE 103 01 493 A1 and DE 102 03 621 A1.

It is the principal object of the present invention to provide an adjusting device for a camshaft of an internal combustion engine which permits use in any field of application while being cost-effective and simple to manufacture.

SUMMARY OF THE INVENTION

In an adjusting device for a camshaft of an internal combustion engine, having a drive element which is driven by a crankshaft of the internal combustion engine, an output element which drives the camshaft of the internal combustion engine, and an actuating element controlled by a brake so as to provide for a relative rotation between the drive element and the output element by varying the braking torque effective on the actuating element.

A substantial advantage of the invention is that the adjusting device can be used for all applications and all phase angle ranges since the actuating range is theoretically unlimited by virtue of the use of a planetary gear mechanism.

The phase angle between the drive element and the output element is advantageously adjusted exclusively by means of a brake. The electrically adjusted brake does not require a power output stage in the control device since the currents which are necessary with the interposition of a high-ratio planetary gear mechanism are very low. A hysteresis brake whose brake torque is independent of the rotational speed is preferably used.

The adjusting device can advantageously be used in all applications. The originally unlimited actuating range can be adapted to particular application by means of a stop.

With a suitable selection of the transmission ratio of the planetary gear mechanism there is advantageously no need for a restoring spring, i.e. one adjusting element, in this case the brake, is sufficient for the adjustment in both directions. If the adjusting device is however configured for particularly high actuation dynamics, the load torque of the camshaft can be increased by an actuating spring in order to implement an optimum adjusting speed of the camshaft adjuster in one direction when the brake is released.

The adjusting device is advantageously embodied as two planetary gear mechanisms which are coupled to one another and which have common elements, so that certain components can be eliminated. This results in a narrow design of the adjusting device which permits a space-saving arrangement.

The invention will become more readily apparent from the following description of exemplary embodiments, thereof on the basis of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a camshaft adjuster with a drive element, an output element and an actuating element which are embodied as what is referred to as a rotating positive gear mechanism, the actuating element and the output element having the same direction of rotation, with a brake capable of engaging the actuating element,

FIG. 2 shows a camshaft adjuster which is embodied as what is referred to as rotating negative gear mechanism, the actuating element and the output element having opposite directions of rotation, with a brake capable of engaging the actuating element,

FIG. 3 shows a camshaft adjuster with a two-stage, coupled planetary gear mechanism, and with a brake capable of engaging the actuating element,

FIG. 4 shows a camshaft adjuster including an actuating spring disposed between the drive element and the actuating element,

FIG. 5 shows a camshaft adjuster including an actuating spring disposed between the output element and drive element, and

FIG. 6 shows a camshaft adjuster including an actuating spring disposed between the output element and actuating element.

DESCRIPTION OF THE VARIOUS EMBODIMENTS

For the sake of simplicity, the same reference symbols have been used for the designation of corresponding components in the various figures.

FIG. 1 shows an adjusting device 1 for a camshaft 2 of an internal combustion engine for changing the phase angle of the camshaft 2 with respect to a crankshaft (not shown here) of an internal combustion engine according to a first exemplary embodiment, the camshaft 2 being driven by the crankshaft by means of the adjusting device 1.

The adjusting device 1 comprises three elements, specifically, a drive element 3 which is driven by the crankshaft, an output element 4 which is connected fixedly in terms of rotation to the camshaft 2 and which drives the camshaft 2, and an actuating element 5 for adjusting the phase angle between the drive element 3 and output element 4 to which a brake 6 is connected, it being possible to bring about a relative rotation between the drive element 3 and output element 4 by varying the torque at the actuating element 5. The brake 6 is preferably an electromagnetic brake which operates without wear, in particular in a contactless fashion. A hysteresis brake whose torque is independent of the rotational speed is particularly suitable. The currents which are required to actuate the brake 6 are so low that no power output stage is needed in the control device. The brake 6 may be a single-acting brake or a multiple-acting brake. The rotor (not shown here) of the brake 6 is connected fixedly in terms of rotation to the actuating element 5. It is also not shown that the housing (stator) 7 of the brake 6 is supported on a stationary component of the internal combustion engine such as, for example, a cylinder head, cylinder head cover, control casing cover etc. The drive element 3 is embodied in the present case as a chain gear which is driven by the crankshaft of the internal combustion engine via a drive chain (not illustrated here).

In order to permit the adjusting device to be used in any field of application, a design of the adjusting device 1 is described which permits any desired phase angles between the drive element 3 and output element 4.

The adjusting device 1 is preferably embodied as a gear mechanism and in particular as a planetary gear mechanism, and in this case the three elements 3 to 5 of the adjusting device are each embodied as one of the elements of the planetary gear mechanism.

According to FIG. 1, the elements 3 to 5 of the adjusting device 1 are embodied as a single-stage planetary gear mechanism. A planetary gear mechanism is composed of a ring gear 3, planet gears 8, a sun gear 5 and at least one planet carrier 4, which forms the output element. The output element 4 comprises the two planet carriers in which the planetary gears 8 are mounted by means of bearing bolts 9 with their axes 10 extending parallel to the axis 12 of the adjusting device 1. Three planetary gears 8, which are surrounded on the outside by the drive element 3 which forms the ring gear, are preferably provided, said planetary gears 8 meshing with the drive element 3. In the center, the planetary gears 8 run on the actuating element 5 which is embodied as a sun gear. The shaft 11 of the actuating element (sun gear) 5 is also the common axis 12 of rotation for the drive element (ring gear) 3 in this exemplary embodiment, and the output element (planet carrier) 4. On the output side, the planetary gears 8 are connected to the camshaft 2 via the planet carriers 4. In this case, the elements 3 to 5 of the adjusting device 1 are embodied as positive gear mechanisms, i.e. assuming the chain wheel 3 to be stationary the actuating element 5 and camshaft 2 rotate in the same direction.

The adjustment of the phase angle between the drive element 3 and output element 4 is brought about exclusively by means of the brake 6, specifically by varying the braking torque at the actuating element 5. In order to bring about a constant phase angle between the chain wheel 3 and camshaft 2, the brake 6 acts correspondingly on the actuating element 5. Varying the braking torque increases or respectively reduces the rotational speed of the actuating element 5, causing the phase angle of the camshaft 2 to change relative to the crankshaft.

FIG. 2 shows an adjusting device 1 according to a second exemplary embodiment. The adjusting device 1 is also embodied as a single-stage planetary gear mechanism. The drive element (chain gear) 3 forms the two planet carriers in which planetary gears 8 are mounted by means of bearing bolts 9 with their axes 10. Three planetary gears 8 are preferably provided, which are surrounded on the outside by the output element (camshaft) 4 which forms the ring gear, said planetary gears 8 meshing with the output element 4. In the interior, the planetary gears 8 run on the actuating element 5 which is embodied as a sun gear. The shaft 11 of the actuating element (sun gear) 5 has a common axis 12 of rotation with the output element (ring gear) 4 and the drive element (planetary gear carrier) 3. On the output side, the ring gear (output element) 4 is formed integrally with the camshaft 2. In this case, the elements 3 to 5 of the adjusting device 1 are embodied as negative gear mechanisms, i.e. assuming the chain wheel 3 to be at standstill the actuating element 5 and camshaft 2 rotate in opposite directions.

A phase shift of the camshaft 2 is brought about by varying the braking torque at the actuating element 5. The transmission ratio is preferably selected such that, when there is a constant phase angle between the drive element 3 and output element 4, the actuating element 5 is braked to a specific rotational speed which is equal to the rotational speed of the camshaft 2. Increasing the braking torque reduces the rotational speed of the actuating element 5 (if appropriate as far as the stationary state) and causes the camshaft 2 to be advanced with respect to the chain wheel 3. If the braking torque is reduced (if appropriate as far as zero, i.e. “actuating element free”) the actuating element 5 is accelerated by the load torque of the camshaft 2 and the camshaft 2 is thus retarded with respect to the chain wheel 3.

FIG. 3 shows an adjusting device 1 according to a third exemplary embodiment. The adjusting device 1 is embodied as a two-stage, coupled planetary gear mechanism, both planetary gear mechanism units having common elements 5, 8. Each planetary gear mechanism unit has it own ring gear structure 3, 13 with internal toothing 14, 15 and each shares both the sun wheel 5 and the planet gears 8 with the other planetary gear mechanism unit, the drive-side ring gear being formed by the chain wheel 3. The ring gears 3, 13 mesh with their toothings 14, 15 with the planet gears 8. The planet gears 8 are arranged distributed circumferentially in the space between the ring gears 3, 13 and the actuating gear element 5 which is a sun gear, i.e. the planet gears 8 are merely inserted loosely without particular bearing. The planet gears 8 are guided axially by an abutment disk 16 which is connected to the chain wheel 3, and an output element 4 which is formed on the camshaft 2 and is firmly connected to the output-side ring gear 13. The planet gears 8 mesh with the actuating element 5. The axis of the shaft 11 of the actuating element (sun gear) 5 is also the axis 12 of rotation for the drive-side ring gear 3 and the output-side ring gear 13. In this case, the adjusting device 1 can be embodied either as a positive gear mechanism or as a negative gear mechanism, depending on the number of teeth of the two ring gears 3, 13. After the number of teeth of the ring gears 3, 13 has been defined it is possible to make a negative gear mechanism from a positive gear mechanism, and vice versa, by exchanging the two ring gears 3, 13.

However, if the adjusting device 1 according to the invention is to be configured for particularly high actuating dynamics, the effective load torque of the camshaft 2 can be decreased or increased by means of an actuating spring 17 according to the FIGS. 4 to 6 in order to implement an optimum actuating speed of the adjusting device 1 when the braking torque varies.

A plurality of possible arrangements of the actuating spring 17 is conceivable. FIG. 4 shows the actuating spring 17 between the drive element (chain wheel) 3 and actuating element (brake) 5, FIG. 5 shows the actuating spring 17 between the drive element (chain wheel) 3 and the output element (camshaft) 4 and FIG. 6 shows the actuating spring 17 between the output element (camshaft) 4 and actuating element (brake) 5.

If the unlimited actuating range of the adjusting device is to be restricted for a specific application, it is possible to provide a stop limiting the relative rotational movement between for example the drive element 3 and the output element 4, for example a positively locking device element. Such a stop may simply be a projection 3′ extending from the output element 3 into a circumferential recess 4′ formed in the output element 4 over a certain angular range as indicated in FIG. 2. 

1. An adjusting device (1) for a camshaft (2) of an internal combustion engine, including a drive element (3) which is driven by a crankshaft of the internal combustion engine, an output element (4) which is connected to the camshaft (2) of the internal combustion engine, and an actuating element (5) including a brake (6) for generating relative rotation between the drive element (3) and output element (4) by varying the braking torque effective on the actuating element (5), the arrangement permitting the setting of any desired phase angle between the drive element (3) and output element (4).
 2. The adjusting device as claimed in claim 1, wherein the phase angle between the drive element (3) and the output element (4) is adjustable exclusively by means of the brake (6).
 3. The adjusting device as claimed in claim 1, wherein the brake (6) is one of a single-acting and multiple-acting brake.
 4. The adjusting device as claimed in claim 1, wherein the brake (6) is an electrically actuated brake which operates in a contact-free fashion.
 5. The adjusting device as claimed in claim 1, wherein the adjustment of the phase angle can be limited by means of a stop.
 6. The adjusting device as claimed in claim 1, wherein the adjusting device (1) is embodied in such a way that the actuating element (5) and the output element (4) have opposite directions of rotation.
 7. The adjusting device as claimed in claim 1, wherein the adjusting device (1) is embodied in such a way that the actuating element (5) and the output element (4) have the same direction of rotation.
 8. The adjusting device as claimed in claim 1, wherein an actuating spring (17) is effective between two of the three elements (3 to 5) of the adjusting device (1).
 9. The adjusting device as claimed in claim 1, wherein the adjusting device (1) is embodied as a gear mechanism.
 10. The adjusting device as claimed in claim 1, wherein the adjusting device (1) is embodied as at least one planetary gear mechanism.
 11. The adjusting device as claimed in claim 10, wherein the adjusting device (1) includes two planetary gear mechanisms (3, 5, 8 and 13, 5, 8) which are coupled to one another, the two planetary gear mechanisms having common elements (5, 8).
 12. The adjusting device as claimed in claim 1, wherein the three elements (3 to 5) of the adjusting device are each embodied as one of the elements of a planetary gear mechanism, the planetary gear mechanism having a ring gear (3, 4, 13), planet carriers (3, 4) and a sun gear (5). 